1. Technical Field
The present invention relates to a sensor module capable of detecting a force component and a force detecting device and a robot using the sensor module.
2. Related Art
There has been known a force sensor disclosed in JP-A-4-231827 (Patent Literature 1) as a force sensor (a sensor device) including a piezoelectric material. Patent Literature 1 discloses a force sensor in which a signal electrode is sandwiched by crystal disks, which are piezoelectric materials, and a measurement element sandwiched by metal cover disks is sealed in a metal ring by welding.
In the force sensor disclosed in Patent Literature 1, it is likely that dimensional errors of the signal electrode, the crystal disks, and the metal cover disks occur. It is also likely that a gap is formed in the welding because of the errors and moisture, the outdoor air, and the like intrude into the gap, whereby charges generated in the crystal disks leak to the outside to disable accurate measurement. Further, there is a problem in that a process for the welding is complicated and it is difficult to apply the process to mass production.
Therefore, a sensor element that prevents a leak and does not depend on a measurement environment can be obtained by using a sensor device shown in FIG. 12.
As shown in FIG. 12, a sensor device 200 as a whole includes a sensor element 214 in which an electrode plate 218 is sandwiched by two quartz plates 216 having the same cut surfaces and opposed to each other, a first member 202 made of metal that houses the sensor element 214, and a second member 204 made of metal that is joined to an upper surface 224, which is the outer circumference of an opening section 220 of the first member 202, and set in contact with the quartz plate 216. A coaxial connector 206 is attached to a side surface of the first member 202. The coaxial connector 206 includes an outer circumferential section 208 and a center conductor 210. Insulative resin 212 is filled between the outer circumferential section 208 and the center conductor 210. The outer circumferential section 208 and the center conductor 210 are electrically insulated. The outer circumferential section 208 is short-circuited with the first member 202 and the second member 204. The center conductor 210 is electrically connected to the electrode plate 218.
The sensor device 200 is sandwiched by pressurizing plates (not shown in the figure) and pressurized. The quartz plate 216 outputs (induces) charges to the electrode plate 218 according to a piezoelectric effect involved in the pressurization. Pressure applied to the quartz plate 216 changes according to an external force applied to the pressurizing plates. Therefore, it is possible to detect an external force applied to the sensor device 200 by monitoring, through the coaxial connector 206, a change amount of output charges due to the change in the pressure.
In the sensor device 200, to prevent the charges induced from the quartz plate 216 from leaking to the outside because of moisture or the like, the sensor element 214 is sealed by the second member 204 in a state in which the inside of the first member 202 is filled with the dry air or a state in which vacuum is maintained in the first member 202.
However, when the sensor element 214 is housed in the first member 202, a problem explained below occurs. In a manufacturing process for the first member 202 and the sensor element 214, the first member 202 and the second member 204 have dimensional errors and the sensor element 214 also has a dimensional error. Therefore, it is difficult to perform adjustment for equalizing the internal height of the first member 202 (the height from a contact surface of the first member 202 and the sensor element 214 to a contact surface on which the first member 202 and the second member 204 are joined) and the height of the sensor element 214.
As explained above, in the sensor device 200, a gap is formed between the sensor element 214 and the second member 204 because of the dimensional errors or the sensor element 214 projects from the upper surface 224 of the first member 202 and the second member 204 presses the sensor element 214. In this state, it is difficult to apply equal pressure to the sensor element 214 using the pressurizing plates.